1. Field of the Invention
The present invention relates to a system for adjusting a laser oscillator, and more particularly, to a system for monitoring power of a laser beam from a laser oscillator and determining an alignment parameter corresponding to a peak value to thereby adjust the laser oscillator.
2. Description of the Related Art
In general, the power of a laser beam emanated from a laser oscillator varies depending on the alignment of the laser oscillator, particularly, on the alignment of resonant mirrors that defines an optical resonator. To oscillate the laser oscillator under the optimal conditions to generate a laser beam of peak power, therefore, it is necessary to align the resonant mirrors and form an optical resonator therebetween.
As such a system for adjusting a laser oscillator is proposed the one shown in FIGS. 1 and 2.
FIG. 1 illustrates a conventional system for adjusting a laser oscillator, which has a laser medium 11 positioned between fixed bases 12-1 and 12-2 arranged to face each other. The fixed bases 12-1 and 12-2 have openings 12a formed in their center portions to permit a laser beam to pass through. Movable bases 14-1 and 14-2 each having a resonant mirror 13 in the center portion are arranged outside the respective fixed bases 12-1 and 12-2. Feed screws 15 and 16 are screwed in the respective two orthogonal corners of each movable base 14-1 or 14-2, with their distal ends abutting on the outer surface of the associated laser beam 12-1 or 12-2, as shown in FIG. 2. A hinge 17 is provided in the lower right corner (in FIG. 2) of one of the movable bases 14-1 and 14-2 and the facing corner of the other movable base between the fixed bases 12-1 and 12-2, so that the movable bases 14-1 and 14-2 can tilt in two perpendicular directions (hereinafter simply referred to as "X direction" and "Y direction") about these corners. Therefore, rotating one of the feed screws, 15, will tilt the movable bases 14-1 and 14-2 and the resonant mirrors 13-1 and 13-2 provided integral with the movable bases in the Y direction, and rotating the other feed screw 16 will tilt the movable bases 14-1 and 14-2 and the resonant mirrors 13-1 and 13-2 in the X direction.
The feed screws 15 and 16 respectively for the Y and X axes, which are provided on the movable base 14-1 (on the right-hand side in FIG. 1), have knobs 19 that permit the feed screws 15 and 16 to rotate. To the Y-axis and X-axis feed screws 15 and 16 provided on the other movable base 14-2 (on the left-hand side in the diagram) are coupled a Y axis driving motor 21 and an X axis driving motor 22, respectively, to drive forward and backward the associated feed screws 15 and 16.
The movable base 14-1 on the right-hand side in the diagram has an opening 14a formed in the center portion, through which a laser beam passing through the resonant mirror 13-1 provided in the center portion is guided outside. The laser beam 24 led out through the opening 14a enters a power detector 27 via a beam splitter 26, and its power is detected there.
Data of the laser power detected by the power detector 27 is sent to a comparator 28 where it is compared with a previously set peak value. The result of the comparison is input to a central processing unit 31. Based on the discrimination result, the central processing unit 31 sends a control command to a Y axis motor drive instructing section 33 for the Y axis driving motor 21 or an X axis motor drive instructing section 32 for the X axis driving motor 22 to acquire a peak value.
In the system shown in FIG. 1, the alignment of the resonant mirrors 13 of the laser oscillator is adjusted as follows. First, the resonant mirror 13-1 is positioned perpendicular to the optical axis of the laser beam 24 and fixed there by manipulating the knobs 19 of the feed screws 15 and 16 of the movable base 14. Likewise, the resonant mirror 13-2 is temporarily adjusted perpendicular to the optical axis. After such temporary adjustment is finished, the laser oscillator is activated as follows to start the real adjustment. It is known that in the laser oscillator, the light emanating from the laser medium 11 is repetitively reflected between the resonant mirrors 13-1 and 13-2 to be oscillated, and is output as the laser beam 24 passing through one of the resonant mirrors 13-1. This laser beam 24 is detected by the power detector 27, and the detection data is sent out to the comparator 28. This data is compared with the predetermined peak value to discriminate whether or not it is the peak value, before it is input to the central processing unit 31. The central processing unit 31 activates the X axis driving motor 22 and Y axis driving motor 21 via the respective X axis and Y axis motor drive instructing sections 32 and 33 to adjust the position of the other resonant mirror 13-2. In other words, the central processing unit 31 sends operation instructions reflecting the rotational direction and the amount of rotation of the X axis and Y axis driving motors 22 and 21 to the X axis and Y axis motor drive instructing sections 32 and 33 in accordance with the input value. As a result, the resonant mirrors 13 are tilted slightly in a predetermined direction. The peak value of the laser power is detected by repeating the above-described operation. That is, the peak value of the laser power is found by a control system which expects the peak value at a certain single point as described above.
This adjusting method, however, gives rise to the following shortcoming. According to this method, adjustment is conducted on the assumption that the peak value lies on a certain single point, and no judgment is made on where on the overall output distribution the current output corresponds. It therefore takes time to reach the peak value, impeding to speeding up the adjustment of the peak value. If this process is performed every time the laser is changed, the time for the intended operation of the laser oscillator would undesirably become shorter.
The laser output has a fluctuation width (hereinafter called "ripple"), so that when the laser output at one point on the output distribution is measured, the peak value of the ripples may be erroneously judged as the peak value of the laser output power.
Further, the laser output will vary depending on the environmental conditions, such as temperature and vibration, under which the laser is used, so that a user should always perform the scanning of the peak value while monitoring the environment. Furthermore, the peak value varies from one product to another of the same kind, requiring a control method or a certain value designed specifically for each product.
In short, it is difficult to improve the speed for the conventional adjustment of the peak value of the laser power and it is possible that the peak value of the ripples is mistaken for the peak value of the laser output power. In addition, the scanning of the peak value cannot be spontaneously dealt with when the laser output changes due to a change in the environmental conditions, and the conditions for scanning the peak value vary between products of the same kind.